Three-dimensional (3-D) objects, such as prototype parts, may be produced directly from computer-aided design (CAD) databases. Various technologies may be used to produce such objects, including layered additive processes. Current layered fabrication methods for building metallic parts typically use polymer binders mixed with metal powder. For example, in FDM (Fused Deposition Method) fabrication, a mix of polymer binder and metal powder is made into a filament which is fed through a heated extrusion nozzle. A green (unsintered) part is then formed by layer-by-layer extrusion of the material. In SLS (Selective Laser Sintering), a mix of loose powder (polymer and metal or polymer-coated metal) is spread into a thin layer and exposed to a laser which melts the polymer particles and bonds the metal powder in selected areas of each layer to form the green part. Other techniques use similar approaches with some variations. The green part is then sintered in a conventional sintering furnace where the fugitive polymer is eliminated.
There are several problems with the approaches described above. Use of polymer binders adds greatly to the sintering shrinkage factor. Also, the creation of dense metallic parts is difficult because of the existence of the binder in the green part structure. Furthermore, incineration of polymer binders during sintering may leave hard-to-remove residues on sintering furnaces and may present environmental hazards.
There are commercial processes for layered fabrication that use binderless metal powder. However, these methods require very expensive high power lasers. Moreover, building parts with overhang features may be problematic with these methods.